학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부(멀티스케일 기계설계전공), 2016. 2. 최만수.나노 입자 조립 기술은 building block인 나노 입자의 직접적인 제어를 통해 구조물을 형성하는 기술로, 이렇게 만들어진 구조물의 독특한 성질로 인해 과학, 공학분야에서 많은 관심을 받으며 연구가 진행되고 있다. Ion-assisted aerosol lithography는 에어로졸 기반의 다목적의 유용한 나노 입자 조립 기술이다. 이러한 ion-assisted aerosol lithography 기술은 그 동안 많은 발전이 있었음에도 불구하고 비전도성 기판에서의 이 기술에 대한 연구는 아직 충분히 이루어지지 않았다. 본 연구에서는 ion-assisted aerosol lithography 방법의 적용 가능성을 확대하기 위해서는 비전도성 기판에서의 이 기술에 대한 심도 있는 이해가 필요함을 느끼고, 이에 대한 연구를 수행하였다.
가장 먼저, 비전도성 기판에서의 나타나는 ion-assisted aerosol lithography 기술의 특성을 파악하기 위한 연구를 수행하였고, 그 결과 비전도성 기판에서는 나노 입자 구조물이 성장과정 중에 성장을 멈추고 후속 입자들이 구조물로부터 밀려나는 현상을 발견할 수 있었다. 전기장 계산을 통하여 이러한 실험 결과를 뒷받침 하였고, 구조물에 축적된 전하에 의해 전기장이 변형되어 추가적인 입자의 증착을 막는 다는 것을 확인 할 수 있었다.
이러한 나노 입자 구조물의 전하 축적을 제어하기 위하여, 이온 트랩을 설계하였다. 이 이온트랩을 이용한 이온 유입량 최적화를 통해, 구조물의 계속된 성장을 유도할 수 있었다. 이러한 이온 유입량 최적화 결과는 나노 입자 구조물과 레지스트 표면의 전하축적에 의한 힘의 균형으로 설명할 수 있었으며, 전기장 시뮬레이션을 통해 이를 확인할 수 있었다.
비전도성 기판에서의 ion-assisted aerosol lithography 기술의 이해를 바탕으로, electrified mask 방법을 대면적의 비전도성 기판에 적용 가능하도록 발전 시켰다. 멀티-스파크 방전기와 대면적의 polymer electrified mask를 이용하여 대면적의 하전된 입자 조립 시스템을 구성하였다. Electrified mask 방법은 정전기적 렌즈 형성에 이온 축적이 필요하지 않기 때문에, 이를 비전도성 기판에 적용하기 위해서 이온트랩을 이용하여 모든 이온을 제거하였다. Electrified mask에 가해주는 전압 값은 전기장 시뮬레이션을 계산을 통하여 얻을 수 있었다. 결론적으로, 이 방법을 통하여 비전도성 기판에서도 electrified mask를 이용한 하전 된 입자 조립이 가능함을 보일 수 있었고, electrified mask에 가해준 전압 값을 제어함으로써 비전도성 기판에서도 집속 정도를 정밀하게 제어할 수 있음을 보였다.Assembly of nanoparticles has grabbed attention as an emerging microfabrication technique for its ability to directly manipulate and structure nanoscale building blocks that have unique size-dependent properties. Ion-assisted aerosol lithography is a versatile and scalable aerosol-based nanoparticle assembly technique. In spite of much development of Ion-assisted aerosol lithography, understanding of it on a non-conducting substrate has not been sufficiently investigated. In this study, we recognized the necessity of understanding about ion-assisted aerosol lithography on a non-conducting substrate for the wide use of this method. Hence, we have investigated the research about ion-assisted aerosol lithography on a non-conducting substrate.
First of all, the characteristics of ion-assisted aerosol lithography on a non-conducting substrate were investigated. Nanoparticle structure growth process on a non-conducting substrate was found to be self-terminate and subsequently, the structures repel incoming nanoparticles and scatter them away. Electric field calculations supported the experimental findings and confirmed that the electric field distortion which was caused by charge accumulation within the structures prevents deposition of additional nanoparticles on them.
In order to control accumulated charges on nanoparticle structures, we designed ion trap to manipulate the ion inflow. Through optimization of ion inflow, we have obtained the continuous growth of three-dimensional nanoparticle structures. The effect of charge accumulation on nanoparticle structures and resist surface was elucidated by electric field simulation.
Based on the understanding of ion-assisted aerosol lithography on a non-conducting substrate, we developed electrified mask method for large area on a non-conducting substrate. Multi-spark discharger and large area polymer electrified mask were used for large area assembly of charged nanoparticles. For the application of electrified mask to a non-conducting substrate, all the ions were eliminated by ion trap because electrified mask does not require ions for generation of electrostatic lenses. Applied electric potential on the electrified mask was calculated by electrified simulation. Consequently, we successfully demonstrated that the electrified mask method is applicable to a non-conducting substrate as well as to a conducting substrate. Moreover, precise control of focusing ratio was also achieved on a non-conducting substrate.Chapter 1. Introduction 1
1.1. Background of Research 2
1.2. Objectives for Research 4
1.3. Scope of Research 5
Chapter 2. Characteristics of ion-assisted aerosol lithography on a non-conducting substrate 7
2.1. Introduction 8
2.2. Experimental concept 9
2.2.1. Ion-assisted aerosol lithography 9
2.2.2. Governing equation of charged nanoparticles during the process of ion-assisted aerosol lithography 13
2.3. Experimental method 16
2.3.1. Fabrication of a non-conducting substrate 16
2.3.2. Particle generation and assembly 17
2.3.3. Electric field simulation 19
2.4. Results and discussion 21
2.4.1. Electrostatic focusing of charged nanoparticles on a non-conducting substrate 21
2.4.2. Electric field distortion during assembly of charged nanoparticles on a non-conducting substrate 23
2.5. Conclusion 27
Chapter 3. Assembly of three-dimensional nanoparticle structures on a non-conducting substrate via ion-assisted aerosol lithography 29
3.1. Introduction 30
3.2. Experimental concept 32
3.2.1. Polarity alternation to prevent termination of three-dimensional nanoparticle structure growth 32
3.2.2. Selective capture of ions using the electrical mobility difference between nanoparticles and nitrogen ions 34
3.3. Experimental method 38
3.3.1. Particle generation 38
3.3.2. Assembly of charged nanoparticles on a non-conducting substrate by using polarity alternation 39
3.3.3. Optimization of ion inflow by the ion trap 40
3.4. Results and discussion 42
3.4.1. Assembly of three-dimensional nanoparticle structures by using polarity alternation 42
3.4.2. Selective capture of ions by using ion trap 45
3.4.3. Assembly of three-dimensional nanoparticle structures growth by optimization of ion inflow 47
3.5. Conclusion 52
Chapter 4. Large area assembly of charged nanoparticles on a non-conducting substrate via electrified mask 53
4.1. Introduction 54
4.2. Experimental concept 56
4.2.1. Controlled electrostatic focusing of charged aerosol nanoparticles via an electrified mask 56
4.2.2. Design of a large area nanoparticle assembly system through multi-spark dischargers and a polymer electrified mask 59
4.2.3. Assembly of charged nanoparticles on a non-conducting substrate through elimination of ions and a polymer electrified mask 62
4.3. Experimental method 64
4.3.1. Particle generation 64
4.3.2. Charged nanoparticle assembly via large area electrified mask 65
4.3.3. Determination of electric potential values at the electrified mask surface 67
4.4. Results and discussion 69
4.4.1. Large area assembly of charged nanoparticles via electrified mask 69
4.4.2. Electric field calculation for the determination of electric potential values at the electrified mask in the case of a non-conducting substrate 75
4.4.3. Charged nanoparticle assembly on a non-conducting substrate by eliminating ions via electrified mask 77
4.4.4. Characteristics of the electrostatic lens formation via electrified mask 85
4.5. Conclusion 88
Chapter 5. Concluding Remarks 89
References 92
Abstract (in Korean) 96Docto
